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Dear Tom and Ray: I just bought a new Mazda, and the owner’s manual states that I should use
0W-20 oil. I wonder if that is too lightweight for summer travel at interstate speeds, and would it
not cause the engine to wear more than using 5W-30? The vehicle is a CX-7 with a 2.5-liter I-4
non-turbo engine. I like getting 100,000-plus miles on my vehicles: I currently have an ’03 Protege
with 120,000 miles and a ’97 Toyota with 140,000, and I would want this CX-7 to get that kind of
use. Please advise on your feelings about this 0W-20 oil.

— Jim

Ray: It’s good stuff. My brother uses it in salads.

Tom: For years now, car manufacturers have been pressuring oil companies to make oil better and
less viscous. And they’ve done it.

Ray: Just because oils are less viscous (thick), that doesn’t mean they don’t lubricate,
dissipate heat or protect well against wear and tear. It just means they do all that stuff while
creating less friction, which means you get better mileage and longer engine life.

Tom: You’re probably not old enough to remember when cars routinely took 40-weight oil in the
summer and 20-weight oil in the winter. That stuff was real sludge. You could still see the
dinosaur bones in it.

Ray: Then, multiviscosity oils were invented. So, for instance, you could use a 10W-40 oil that
would act like a 10-weight (thinner) oil when the temperature was low and a 40-weight (thicker) oil
when the temperature was high.

Tom: And, through the years, as lubricant technology has improved, the viscosity of the oils has
dropped, to the point where we can now use a zero-viscosity oil in cold weather. That means the
engine uses less energy to push its parts through the oil. That energy goes into miles per gallon
instead.

Ray: It also means the oil coats the inside of the engine more quickly — in a fraction of a
second after startup — which protects the engine from wear and tear during cold starts and makes it
last longer. It also means the engine starts more easily in cold weather. Pretty good stuff,
huh?

Tom: We’ve seen no problems as cars have gone from 10W-40 down to 5W-20. And although the 0W-20
is fairly new, I don’t expect any problems from that, either.

Ray: That said, most vehicles have “severe duty” recommendations in the owner’s manual. They’ll
tell you that if you’re planning to climb Pikes Peak with a trailer, if you’re using your car as a
taxi, or if you live where it’s regularly above 100 degrees out, you qualify for special
maintenance procedures. Those can include more-frequent oil changes and/or use of a different
oil.

Tom: So, if that describes you, Jim, check your owner’s manual and look up the severe-duty
recommendations. But if you’re just driving the car like the rest of us, I’d go with what the
manufacturer suggests.

Have a question about cars? Write to Click and Clack Talk Cars in care of King Feature
Syndicate Group, 300 W. 57th St., New York, NY 10019.